Angular divider devices and toolholder turrets for angularly displacing a workpiece or a tool mounted thereon through a predetermined angular movement for passing from one working position to another in accordance with a predetermined program generally governed by electrical or electronic means or again by hydraulic, magnetic and similar governing devices are known. In such known devices, blocking means are generally situated in the various predetermined positions and may include fixed and mobile crown gear wheels which engage with one another, thus holding the position fixed during the working phase, and positioning means consisting generally of slots distributed along the rotational path and latches, bolts, pins or the like which are raised and introduced into said slots at each change of position of the workpiece carried by the apparatus.
While blocking in an exact position achieved by said crown gear wheels engaging with one another is entirely satisfactory for normal machining operations, the movement phase and the prepositioning of the movable part of the apparatus carried out with such known means presents numerous disadvantages which restrict the use of the apparatus.
A first disadvantage arises from the necessity of being able to have only a limited number of working positions available, due to the fact that both said positioning slots and also the latches, bolts, pins or the like with the relative extraction, insertion and control means, have dimensions in the circumferential direction which are of the order of several millimeters. For this reason, it is not possible to obtain very closely spaced angular positions. In the case where it is necessary to have available a divider with numerous positions, it is necessary to increase appreciably the diameter of the path of the slots with consequent unacceptable increase in weight and cost. A second disadvantage of the known divider devices arises from the positioning means themselves which, since they must arrest the movable part in a predetermined position, must have opposing surfaces perpendicular to the direction of movement to create a positive and rigid stopping or latching up to the instant of blocking said gear wheels in position. Such rigid stopping gives rise to an impact between the movable part and the fixed part, which is proportional to the velocity, weight, inertia, etc., of the movable part. For this reason it is necessary to create decelerations, reversals of movement and the like with a reduction in the velocity of rotation and therefore an increase in production times. Moreover, such mechanical prepositioning means are complicated and sensitive and frequently subject to wear and disadvantages of various types.
Also known are other types of divider devices which do not possess prepositioning means of the slot and latch type as in the aforementioned types, but are equipped for this purpose with an appropriate motor of electrical, hydraulic or similar type, which provides for the rotation of the movable part up to the predetermined position and in addition have to be equipped with further actuating means for blocking the movable part in the working position on the fixed part by closure of the two crown gear wheels, such further means being generally constituted of a further electrical or similar motor, or of a piston-cylinder fluid unit, elastic means or other means.
Such known types possess, nevertheless, other disadvantages. For example at least two separate actuating means must be made available, one for the movement and the other for the closure, which two means, if they are both constituted of separate motors of electrical, pneumatic or the like type, lead to a notable increase in cost, bulk and weight and can also require separate supplies with further consequent increase in cost. If, instead, the closure means is constituted of a fluid-actuated piston-cylinder group (with hydraulic or pneumatic fluid) or of springs or the like, a further disadvantage is encountered deriving from the compressibility and/or elasticity intrinsic in the fluid or in the springs, which causes a reduction in stiffness of the movable part relative to the fixed part, permitting movements both on axial planes due to eccentric forces acting upon the piece being worked upon or upon the tool in work, and upon planes perpendicular to the axis due to tangential thrusts, said last-named movements being capable of acting upon the flanks of the teeth of the crown gear wheels in contact and therefore of causing axial loadings which are transmitted finally to the fluid or to the predetermined elastic means for maintaining the closure stable.